Electrochemical cells are known (referred to as “ZEBRA” cells) which include a molten alkali metal anode; an electrically insulative solid separator that functions as an alkali metal ion-conducting solid electrolyte; a salt electrolyte (referred to herein as a “catholyte”) in a cathode compartment which is at least partially molten at the operating temperature of the cell; and a cathode. Electrochemical cells of this type are useful as energy storage devices, particularly when a plurality of cells are arranged to form a module or battery pack.
Commonly used cells employ NiCl2 as the active material in the cathode. However, Ni is expensive and such batteries have a high operating temperature (˜350° C.). The use of FeCl2 as the active material in the cathode has been proposed, but it has not been considered for commercialization due to technical hurdles in raw material handling during fabrication of the cell. For example, a Na/NiCl2 battery can be assembled in the discharged state, which only requires handling of NaCl and Ni powder. However, a Na/FeCl2 battery requires assembly in the charged state means handling highly pyrophoric Na metal and FeCl2. In addition, the FeCl2 used for making the cathode is obtained by chlorinating Fe powder under a chlorine environment. A main reason for using chlorinated FeCl2 to make the cathode is that the surface electrochemical activities of Fe powder are blocked by passivation layers (e.g., various iron oxide and hydroxide species).